The present invention relates to a journal plain bearing in which a bearing alloy layer is provided on a back metal, and more particularly to a plain bearing in which the wear resistance and anti-seizure property are improved.
For example, in a plain bearing used in an engine for a vehicle, a taper-shaped crowning shown by reference symbol xe2x80x9cCxe2x80x9d in FIG. 10 is provided in both of the axially end portions of a bearing face. The reason why the crowning C is provided is explained below.
FIG. 11, for example, shows a bearing structure in the side of the large end portion of a connecting rod. The connecting rod 1 acts to receive the combustion pressure of a fuel from a piston and to transmit the combustion pressure to a crank side. In the connecting rod 1, a plain bearing 3 is provided in the large end portion 2, and a crank pin 4 is supported by the plain bearing 3. The crank pin 4 is bent to have a circular arc shape due to the combustion pressure applied thereto from the connecting rod 1, which causes the crank pin 4 to abut on both end portions of a bearing face in the plain bearing 3. In this case, in FIG. 11, the deflection of the crank pin is exaggeratedly depicted.
In a case where the crank pin 4 abuts on both of the end portions of the plain bearing 3, the thickness of a lubricating oil film in the portions is reduced, and the oil film is apt to be broken due to a load fluctuation, a rotational speed fluctuation or the like. Further, in a case where the oil film breakage occurs, a so-called metallic contact that both of a bearing alloy layer 5 of the plain bearing 3 and the crank pin 4 are in direct contact with each other is caused, so that the premature wear and seizure of the plain bearing are apt to occur. Thus, in conventional plain bearings, the crowning C shown in FIG. 10 is provided in each of the end portions of the plain bearing 3 so as to prevent the plain bearing 3 from abutting against the end portions of the plain bearing 3 even when the crank pin 4 is bent, thereby preventing the premature wear and seizure thereof.
Regarding recent plain bearings, the present inventors have found a phenomenon explained below. FIG. 12 shows the variation of an oil film thickness along an axial direction of the plain bearing 3, which variation is theoretically calculated while taking the elastic deformation of both of the plain bearing 3 and the large end portion 2 into consideration (, in which calculation the deflection of the crank pin 4 is neglected). According to this, the oil film thickness becomes maximum at a center portion of the axial length of the plain bearing 3 (, that is, around a location shown by xe2x80x9c0xe2x80x9d) and becomes smaller as approaching each of the axial ends thereof from the center portion. This is because the largest load is applied to the axial center portion of the plain bearing 3 with the result that an oil film pressure becomes highest in the axial center portion in the same manner as that of the oil film thickness distribution, so that the bearing face of the plain bearing 3 is deformed to have a concave shape of a circular arc in such a manner as the axial center portion of the plain bearing 3 comes to be deepest in depth for the reason disclosed below. In a case where the bearing face is deformed in the manner explained above, the crank pin 4 comes to abut both end portions of the plain bearing 3.
As regards the main reasons why the bearing face of the plain bearing 3 is deformed in the manner explained above, the present inventors have found the following two reasons. One of them is that the bearing alloy layer 5 constituting the bearing face is formed of an Al alloy, a Cu alloy or the like which is comparatively soft. Thus, the bearing alloy layer 5 is elastically deformed in the thickness direction in a manner that the axial center portion thereof becomes deepest in depth in the elastic deformation to which axial center portion the largest oil film pressure is applied.
Another of them is a light weight design of the engine for recent vehicles. That is, due to the light weight design of the engine, the aluminum alloy is used in many members constituting the engine, or a bearing housing portion for securing the bearing is made to be thin in thickness. This light weight design is also applied to the connecting rod 1, so that a rigidity of the large end portion 2 tends to be reduced. Further, due to this reduction of the rigidity, the large end portion 2 finally receiving the load applied to the plain bearing 3 is elastically deformed, so that the whole of the plain bearing 3 is elastically deformed in the radial direction thereof to thereby have a convex shape such as that of a barrel. Thus, the bearing face itself is deformed to have an arcuate, concave shape in axial cross section.
However, since the conventional crowning C is provided for compensating the deflection of the crank pin 4, it is impossible to address the problem of the unfavorable abutment occurring due to the elastic deformation of the bearing alloy layer 5 and/or the elastic deformation of the large end portion 2 of the connecting rod 1, so that there occurs the problem that it is impossible to avoid the occurrence of the premature wear and/or the seizure. As means for addressing the problem, it appear advisable to increase in the axial direction an area forming the crowning C. However, since the area in which the lubricating oil film is formed is reduced insofar as this means is concerned, a load-receiving area is reduced with the result the true specific load of the bearing is increased unfavorably, so that the load capacity of the bearing becomes reduced to an unacceptable degree.
The present invention is achieved by taking the matter explained above into consideration, and an object of the invention is to provide a plain bearing which can prevent a shaft from abutting against the end portions of the plain bearing due to the elastic deformation of the bearing alloy layer and/or of the bearing housing, while suppressing the decrease in the load-bearing capacity of the plain bearing.
According to the first aspect of the present invention, there is provided a plain bearing comprising a back metal, a bearing alloy layer bonded onto the back metal, said bearing alloy layer having:
a cylindrical bearing face present on a side of a surface of said bearing alloy layer;
an end portion present at each of axially terminal sides of said bearing alloy layer;
at least one inclination face provided at each of said end portions, which inclination face is extended from an axially predetermined location of said bearing face to the end portion of the bearing alloy layer so that said inclination face is tilted radially outwardly of said cylindrical bearing face from said axially predetermined location toward said end portion and so that axial length of said inclination face is varied along a circumference of said cylindrical bearing face.
In the plain bearing according to the first aspect of the invention, since at least one inclination face inclined radially outwardly from the axially predetermined location defined between both ends of a bearing face toward the end of the bearing face is formed in each of the axially terminal sides of the bearing face in such a manner as to have different, axial lengths in respective portions defined along the circumference of the cylindrical bearing face, it is possible to compensate the elastic deformation of the bearing alloy layer and/or the bearing housing. That is, since the axial length of the inclination face along the circumference of the bearing face are selected to compensate the elastic deformation varying along the circumference of the bearing face, it is possible to minimize the area in which the inclination face is provided. Accordingly, it is possible to compensate the elastic deformation of the bearing alloy layer and/or the bearing housing while suppressing the decrease in the load capacity of the plain bearing, and it is possible to prevent the premature wear and the seizure.
According to the second aspect of the invention, there is provided a plain bearing set forth in the first aspect of the invention, in which the axial length of the inclination face is longest at an axially extended portion of the bearing face at which portion an oil film pressure becomes maximum, and in which plain bearing the axial length of the inclination face decreases as being spaced apart circumferentially from the location of the maximum oil film pressure. That is, in a case where the rigidity of the bearing housing is relatively low in the axial direction of the plain bearing, the axial length of the inclination face is selected so that the axial length thereof may become longest at the portion having a maximum oil film pressure in the bearing face and so that the axial length thereof may be decreased as being spaced apart therefrom in the circumferential direction. In the case of the plain bearing, the bearing face of the plain bearing is deformed in a arcuate concave shape in axial cross section with a deepest position being present at the maximum oil film pressure portion, however, according to the structure of the second aspect of the invention the axial length of the inclination face is made to be longest at the maximum oil pressure portion, so that it is possible to minimize the abutting of the shaft against both axial end portions of the bearing face.
According to the third aspect of the invention, there is provided a plain bearing set forth in the first aspect of the invention, in which the axial length of the inclination face is shortest at an axially extended portion of the bearing face at which portion an oil film pressure becomes maximum, and in which plain bearing the axial length of the inclination face increases as being spaced apart circumferentially from the location of the maximum oil film pressure. That is, in another case where the rigidity of the bearing housing is relatively high in the axial direction of the plain bearing (as shown in FIG. 6), the degree of the elastic deformation of the concave shape occurring at the maximum oil pressure portion of the bearing face is small, so that the axial length of the inclination face can be made to be short at the portion having a maximum oil film pressure in the bearing face. Thus, since the area of a bearing face portion adapted to bear the load of the shaft can be increased at the maximum oil film pressure portion, it is possible to make the axial length of an inclination face portion other than that of the maximum oil film portion long so that the bearing area of the bearing face may be reduced. Since, in the bearing face portions (other than the maximum oil pressure portion) in which the axial length of the inclination face is increased, it is possible to reduce the area of the bearing face adapted to receive a shearing resistance of the oil film without large decrease in the load-bearing capacity of the plain bearing, it is possible to reduce the friction loss of the plain bearing.